It has taken 50 years, rather longer than the running time of one of his famous horror films, but Alfred Hitchcock's most enduring whodunit appears to have been finally solved.
Scientists at Louisiana State University claim to have discovered why thousands of seagulls began killing themselves along the coast of northern California in the summer of 1961.
The mysterious avian deaths, in which many of the birds flew Kamikaze-style into houses along the Monterey Bay shore, south of San Francisco, were cited as one of the major inspirations for Hitchcock's 1963 film The Birds.
Now, marine biologists who have been conducting post-mortem examinations of seabirds killed during the 1961 incident have reached a credible conclusion about their deaths: they were poisoned.
Writing in the latest edition of the journal Nature Geoscience, the researchers say they examined the stomach contents of seagulls and turtles collected during the period and discovered unusual quantities of a nerve-damaging toxin called domoic acid.
The acid, which most likely came from anchovies and squid which formed part of the birds' natural diet, can sometimes cause brain damage.
In severe cases, it leads to them becoming confused, suffering seizures, and dying.
Sibel Bargu, who led the research, said domoic acid was found in 79 per cent of the plankton ingested by anchovies and squid.
Over a short period that would become sufficiently concentrated to cause fatal injuries to predators who ate them.
Although this has previously been cited as a potential explanation for the 1961 event, there has been no evidence to support it until now.
"Here we show that plankton samples from the 1961 poisoning contained toxin-producing Pseudo-nitzschia, supporting the contention that these toxic diatoms were responsible for the bird frenzy that motivated Hitchcock's thriller," she writes.
A similar toxic bloom caused avian deaths in the same area in the 1990s, and in 1989 domoic acid was found to have contaminated mussels which killed four people on Prince Edward Island in Canada.
The spectacle of the dying birds was witnessed by Hitchcock, who took other elements of the film's plot from a Daphne du Maurier novel called The Birds.